Using CGS4 on UKIRT, we have obtained a 1.95-2.45 micron infrared spectrum of the primary candidate counterpart to the bright Z low-mass X-ray binary (LMXB) GX5-1. IR photometry by Naylor, Charles, & Longmore (1992) and the astrometry of Jonker et al. (2000) had previously identified this star as the most likely counterpart to GX5-1. The spectrum presented here clearly shows Brackett γ and He lines in emission, for the first time confirming the identity of the counterpart. Similar to our previous spectroscopy of the Z LMXBs Sco X-1 and Sco X-2 (Bandyopadhyay et al. 1999), the K-band spectrum of GX5-1 shows emission lines only, possibly indicating that the spectral type of the mass donor is earlier than G5. We discuss the implications of this spectrum for the nature of the Z LMXBs.